The present invention relates to a control apparatus and a control method for vehicle-mounted internal combustion engines, and more particularly to improvement of drivability when the control of the engine is shifted from a fuel cutoff control, which is performed during deceleration of the vehicle, to resumption of fuel supply.
As is well known, in many a vehicle-mounted internal combustion engine, a fuel cutoff control, which means a temporary suspension of fuel supply to the internal combustion engine at the time of deceleration of the vehicle speed, is performed with a view to improving the engine's fuel efficiency. According to a technique disclosed in Hatsumei Kyokai (Japan Institute of Invention and Innovation), Report on Published Techniques (in Japanese), No. 2002-3784, during a fuel cutoff control, the opening degree of a throttle valve (throttle opening degree) is controlled to be greater than the usual target opening degree when the accelerator pedal is not depressed (throttle opening increase control). This is intended to reduce the compressive reaction force and thereby to reduce the engine braking force due to pumping. As a result, the degree of deceleration of the vehicle is appropriately controlled, and the shock due to the down shifting of the transmission is suppressed.
However, execution of the throttle opening increase control during a fuel cutoff control involves the risk of the following trouble. Thus, when the opening degree of the throttle valve is varied, the corresponding variation air flow lags behind. Consequently, when a fuel cutoff control is discontinued to resume fuel supply during the throttle opening increase control, even if the throttle opening degree is controlled in the closing direction simultaneously with the resumption of fuel supply, a greater quantity of air than is appropriate will be let into the cylinders immediately after the resumption of fuel supply. As a result, the engine will generate a greater running power immediately after the resumption of fuel supply than is intended by the driver, inviting troubles such as deteriorated drivability. On the other hand, if resumption of fuel supply is delayed until the quantity of air let into the cylinders becomes stabilized to prevent these troubles, the responsiveness of the running power will be correspondingly affected, again inviting deteriorated drivability.